In Freud's writings it is difficult to discern any systematic distinction between the three related terms 'ego-ideal' (Ich-ideal), 'ideal ego' (Ideal Ich), and superego (‹ber-Ich), although neither are the terms simply used interchangeably. Lacan, however, argues that these three 'formations of the ego' are each quite distinct concepts which must not be confused with one another.
In his pre-war writings Lacan is mainly concerned to establish a distinction between the ego-ideal and the superego, and does not refer to the ideal ego.
Although both the ego-ideal and the SUPEREGo are linked with the decline of the Oedipus complex, and both are products of identification with the father, Lacan argues that they represent different aspects of the father's dual role.
The superego is an unconscious agency whose function is to repress sexual desire for the mother, whereas the ego-ideal exerts a conscious pressure towards sublimation and provides the coordinates which enable the subject to take up a sexual position as a man or woman (Lacan, 1938: 59-62).
In his post-war writings Lacan pays more attention to distinguishing the ego-ideal from the ideal ego (Fr. moi idÈal. Note: at one point, in 1949, Lacan uses the term je-idÈal to render Freud's Ideal-Ich [E, 2]; however, he soon abandons this practice and for the rest of his work uses the term moi idÈal.). Thus in the 1953-4 seminar, he develops the OPTICAL MODEL to distinguish between these two formations. He argues that the ego-ideal is a symbolic introjection, whereas the ideal ego is the source of an imaginary projection (see S8, 414).
The ego-ideal is the signifier operating as ideal, an internalised plan of the law, the guide governing the subject's position in the symbolic order, and hence anticipates secondary (Oedipal) identification (Sl, 141) or is a product of that identification (Lacan, 1957-8). The ideal ego, on the other hand, originates in the specular image of the mirror stage; it is a promise of future synthesis towards which the ego tends, the illusion of unity on which the ego is built.
The ideal ego always accompanies the ego, as an ever-present attempt to regain the omnipotence of the preoedipal dual relation. Though formed in primary identification, the ideal ego continues to play a role as the source of all secondary identifications (E, 2). The ideal ego is written i(a) in Lacanian algebra, and the ego ideal is written I(A).

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Ego-Ideal (Freud):
The ideal of perfection that the ego strives to emulate. For Freud, the ego-ideal is closely bound up with our super-ego. The super-ego is "the vehicle of the ego ideal by which the ego measures itself, which it emulates, and whose demand for ever greater perfection it strives to fulfil" ("New Introductory Lectures" 22.65). Given the intimate connection of the super-ego to the Oedipus complex, the ego-ideal is likely "the precipitate of the old picture of the parents, the expression of admiration for the perfection which the child then attributed to them" ("New Introductory Lectures" 22.65). It is also tied up with childhood narcissism (the belief in one's own perfection), which in adulthood can take as its substitute the perfection of the ego-ideal.
Ego-Ideal and "ideal ego"(Lacan):
Lacan makes a distinction between the "ideal ego" and the "ego ideal," the former of which he associates with the imaginary order, the latter of which he associates with the symbolic order. Lacan's "ideal ego" is the ideal of perfection that the ego strives to emulate; it first affected the subject when he saw himself in a mirror during the mirror stage, which occurs around 6-18 months of age (see the Lacan module on psychosexual development). Seeing that image of oneself established a discord between the idealizing image in the mirror (bounded, whole, complete) and the chaotic reality of the one's body between 6-18 months, thus setting up the logic of the imaginary's fantasy construction that would dominate the subject's psychic life ever after. For Lacan, the "ego-ideal," by contrast, is when the subject looks at himself as if from that ideal point; to look at oneself from that point of perfection is to see one's life as vain and useless. The effect, then, is to invert one's "normal" life, to see it as suddenly repulsive.

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The concept of the ego ideal appeared for the first time in Sigmund Freud's "On Narcissism: An Introduction" (1914c). The ego ideal takes the place of the narcissism lost during childhood and promises the possible realization of narcissism in the future. Freud's concept of the ego ideal provided support for other, earlier concepts, such as moral conscience, censorship, and self-esteem, and made possible an original understanding of the formation of a mass movement and its relationship to a leader (1921c).